Automated sawing machines and systems are well known and readily available for a host of different applications. For example, there are many types of computer-controlled sawing systems to which lumber is fed so that it is cut in prescribed lengths and at various angles, according to a cut list entered into the computer. In many prefabricated wood structures, various components thereof are cut and pre-assembled, using automated sawing machines to cut the lumber to various lengths and at various angles at the ends of the pieces. As one example, the web and chord components of wooden trusses are often cut and pre-assembled at a factory and then transported to the construction site for building floors, roof structures, and the like.
Automated sawing systems for cutting the outer chord pieces and the inner web pieces of trusses are highly developed and automated to provide accurate, high speed cutting operations. One such cutting system is known as the "Automaster" saw, model 341, obtainable from Alpine Engineered Products, Inc., Grand Prairie, Texas. In such type of saw, the system is computer controlled to move a number of individual saws and simultaneously cut both ends of a board to desired angles in a single pass through the system. A board is manually loaded on a frontal chain-type material conveyor which transports the board to the cutting area of the system. The board is fed by the material conveyor between a pair of left-hand mounted saws and a pair of right-hand mounted saws, so that the ends of the board can be cut substantially simultaneously. The right-hand set of saws are mounted on a track and can be moved to accommodate different lengths of boards. Further, each of the individual saws can be moved at different angular orientations with respect to the material conveyor so as to saw each end of the board at desired angles as the board moves through the sawing system.
In such type of system, each circular saw blade is mounted directly to an electric motor, and the motor is rigidly fixed to the planar face of a large gear-driven sprocket wheel. The large sprocket wheel is not circular, but is C-shaped with a portion of the middle removed so that the end of a board to be cut can be moved through the saw blade without interference by the sprocket wheel. The inside curved surface of the C-shape wheel is mounted on bearings so that the wheel and the power saw mounted thereto can be rotated about an axis that passes parallel and extends through the plane of to the front face of the saw blade. In this manner, the saw can be angled to different positions and be able to cut through a single point on the board without any corrective horizontal movements of the saw. Importantly, this saw's pivot axis is not physically embodied by a shaft, but rather is in the geometric center of the C-shaped sprocket wheel.
The angular orientation of the saw blade about the pivot axis can be oriented to different positions by turning the sprocket wheel with a gear-drive mechanism. The large sprocket wheel is mounted for rotation with respect to a complicated bearing arrangement that requires lubrication frequently to prevent galling or wear to the curved bearing surfaces. Any wear in the gear or bearing surfaces leads to inaccuracy in the precise angular positioning of the saw blade, as well as slight play or wobble of the saw blade during actual sawing. Further, the entire C-shaped sprocket wheel and saw motor can be moved vertically by way of an electric screw-driven arrangement. In like manner, the entire set of right-hand mounted saws can be moved horizontally by a gear driven assembly. Only the right-hand set of power saws needs to be moved horizontally, toward or away from the left-hand set of power saws to accommodate different lengths of boards.
With regard to the sprocket wheel arrangement for angling each saw blade, the motor and saw blade are fixed to the sprocket wheel such that when moved through an arc of angles, an axis of pivotal movement is parallel to and extends through the plane of the front face of the saw blade. In this manner, to change the saw cut from a thirty degree angle to a forty-five degree angle, only the sprocket wheel and attached saw require angular movement, without a corresponding vertical adjustment of the respective electric screw-mechanisms.
As further noted in connection with the Automaster saw system identified above, the in-feed chain conveyor is constructed such that an operator places a board on an upwardly-angled portion of the conveyor where such board is carried to a knee point, at which point the conveyor is oriented horizontally to carry the board laterally into the sawing system. A chain-driven hold-down assembly. holds the board to the material conveyor during horizontal movement of the board into the sawing system. With this type of structure, while it is convenient for the operator to load the lumber on the conveyor without having to lift it shoulder high, when the board is carried over the transition knee point to the horizontal part of the conveyor, the board often tumbles or is rolled before it is clamped and thus becomes misaligned with respect to the left-hand set of saws and the right-hand set of saws.
The in-feed chain conveyor of the Automaster saw has two sets of parallel feed chains for carrying the board into the sawing system. One chain conveyor can be horizontally moved along the frame with the one set of power saws, toward or away from the other set of power saws, to accommodate different lengths of boards. In order to accommodate short boards, i.e., about two feet and shorter, the pair of parallel chain conveyors must be moved together, adjacent each other, so as to be able to move the short board between the left-hand set of saws and the right-hand set of saws. In practice, it has been found that because of the drive bearing arrangement at the rear of the conveyors and the chain-tensioning linkage at the frontal part of each chain conveyor, such conveyors cannot be moved as close to each other as would be needed to cut very short pieces of wood.
As noted above, one set of power saws is movable horizontally along the frame, as is the corresponding hold-down mechanism and chain conveyor. The power drive for the hold-down mechanism and the movable chain conveyor is a long square drive shaft that extends essentially the length of the saw system. Various in-feed conveyors are driven by the drive shaft using a square tubular member through which the drive shaft extends to rotate the tubular member. The tubular member transfers the torque to the conveyor drive gears. The metal-to-metal driving engagement between the square shaft and square tubular member causes wear, thus requiring eventual replacement. To replace the worn parts, the procedure is time consuming, as much of the in-feed conveyors require disassembly and then corresponding assembly using new, and often expensive parts.
In view of the foregoing, it can be seen that a need exists for further improvements in automated sawing systems to reduce costs, maintenance, increase the speed of operation, and generally provide an overall improvement with respect to accuracy and efficiency.